129-12 Assessing Lithium Potential from the Fish Canyon Tuff, Mineral County near Creede, Colorado

Abstract:

Does the size of volcanic eruptions correlate with higher deposits of lithium (Li)? Roughly 28 Ma ago, one of the most powerful volcanic eruptions—an 8 on the Volcanic Explosivity Index (VEI) — occurred in the present-day La Garita Caldera in Mineral County near Creede, Colorado, to produce the Fish Canyon Tuff (FCT). The FCT is composed of layers of rhyolite, dacite, andesite & welded tuff. These rock types from similar eruption styles in intracontinental settings are known to carry Li, which is critically important since the rapid global transition to clean energy (i.e., electric vehicles & battery storage) has increased demand, necessitating the development of unconventional resources. This research is inspired by the recent discovery of the Li-rich deposit in the 19-16 Ma McDermitt Caldera (MDC), located on the Nevada-Oregon border. This deposit is estimated to contain between 20-40 metric tons of Li worth approximately $1.5 trillion in today’s market. This research attempted to mimic the naturally occurring leeching of lithium from FCT rocks with two separate tests with different acids from a volcanic environment, HCl & H₂SO₄.

The samples were crushed & digested using HF to break down silicates. Initial Li content was found using an Inductively Coupled Plasma - Optical Light Spectrometer (ICP-OES). The FCT andesite had the highest concentration at 0.176 mg/L. THE FCT dacite sample was next at 0.091 mg/L, while the FCT vitrophyre sample was lowest at 0.038 mg/L. The concentrations are tens of thousands of times smaller concentration than found at MDC. After placing the samples in acid-baths & testing again with the ICP-OES, HCl-bathed andesite extracted the highest Li content at 51.203 µg/L. The same rock sample with H₂SO₄ bath yielded a 31.062 µg/L Li content. The dacite sample had the second highest Li yield with its HCl bath yielding 32.516 µg/L. Vitrophyre samples yielded the least Li content at an average of 8.810 µg/L. The depositional environment of the La Garita Caldera is drastically different than the MDC & drainage is a prominent factor. The limited Li potential at La Garita Caldera is most likely due to heavier weathering and erosion from superior drainage channels, lacking the more stagnant, evaporative environment of the MDC despite its high overall eruptive volume.

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